The Auxin Receptor Homologues in Cucumber (Cucumis sativus L.) Perform Overlap and Non-Redundant Fuctions During Fruit Development

Auxin plays a pivotal role in many aspects of plant growth and development. It regulates various developmental processes by modulating gene transcription through a SCF^TIR1/AFB-Aux/IAA-ARF module. In this study, two cucumber auxin receptor genes were cloned and designated as CsTIR1 and CsAFB2 which were homologous to Arabidopsis AtTIR1 and AtAFB2. CsTIR1 contains an F-box region and six leucine-rich repeat (LRR) domains, and is localized in the membrane and nucleus. CsAFB2 comprises an F-box region and seven LRR domains, and is uniquely expressed in the nucleus. Transcriptional analysis of genes in different cucumber organs and ovaries with different treatments shows that CsTIR1 and CsAFB2 perform the similar expression pattern. Overexpressing of CsTIR1 and CsAFB2 in tomato (Solanum lycopersicum, cv Micro Tom) both results in an alteration of early fruit development and seedless (parthenocarpic) fruit formation. The CsTIR1 transgenic lines exhibit severely dwarfed phenotype and alterd leaf morphological characters, while the size of CsAFB2 transgenic lines is between CsTIR1 transgenic lines and wild type. However, phenomena such as stigma out of reach of the stamens and long fruit type of tomatoes were uniquely observed in CsAFB2 transgenic lines. This work provides novel insights into the demonstration of pleiotropic functions of TIR1/AFB protein families during leaf morphogenesis and fruit development of cucumber.